In recent years, consciousness about the environment has been enhanced on a global basis, and there is growing concern about global warming caused by mass consumption of petroleum resources and depletion of petroleum resources resulting from the mass consumption.
Against this background, an imperative need recycling-oriented, environment-responsive materials that are composed of nonpetroleum components such as plant-derived ones (biomass) in particular and will be finally decomposed to water and carbon dioxide in natural environment after use. Among other recycling-oriented, environment-responsive materials, one of the most prospective is polylactic acid.
Under such circumstances, initial efforts in development of polylacted fiber have focused on agriculture materials and civil engineering materials with biodegradability, but now there are growing expectations for large-scale applications such as clothing, hygiene products, bedclothing, and other industrial materials.
Furthermore, polylactic acid fibers are also noteworthy as material for nonwoven fabrics because they general have a high strength and an elongation percentage in good balance as well as a low Young's modulus to serve to provide cloth material with soft texture.
In recent years, new nonwoven fabrics of polylactic acid fiber have been developed as interior finishing materials for automobiles. Other nonwoven fabrics have already been in use for interior finishing of automobiles, but nonwoven fabrics of polylactic acid fibers now offer promising prospects as automobile finishing materials because there is an increased need for replacement of conventional materials with environment-oriented ones in the automobile industry. To this end, there have been studies on nonwoven fabrics including polylactic acid fibers with the aim of providing interior finishing materials for automobiles, resulting in development of nonwoven fabrics composed of polylactic acid and other fibers as well as those made of polylactic acid fibers alone.
Patent document 1, for instance, proposes a needle-punched nonwoven fabric produced from polylactic acid fiber, which is a plant-derived fiber, and polytrimethylene terephthalate fiber.
Furthermore, Patent document 2 proposes a nonwoven fabric produced from short fibers of polylactic acid. The technique described in this Patent document 2 is designed to produce nonwoven fabrics from a polylactic acid with a low dry-heat shrinkability that has undergone heat shrinkage in advance in order to reduce shrinkage during the nonwoven fabric production process. This is because interior finishing materials for automobiles are generally heated at 120 to 180° C. during their molding, and the resulting shrinkage has been feared to cause problems such as warp and deformation.